Southwest Quantum Information and Technology

Coherent state phase estimation based on adaptive photon counting

Presenting Author: Matthew DiMario, University of New Mexico CQuIC
Contributing Author(s): Francisco Elohim Becerra

Optical interferometric measurements are an essential tool in many areas in physics, employing a single mode of light to extract information about the properties of a physical system. Coherent states of light have proven to be very convenient states in such measurements, specifically mapping this information into the phase of these states. The difficulty however, is extracting this information with minimal uncertainty, especially in a single-shot measurement. The Cramer-Rao lower bound (CRLB) is the fundamental limit for this uncertainty, which bounds the estimator variance through the quantum Fisher information for coherent states. A physically realizable single-shot measurement strategy that reaches this limit of precision, or even outperforms an ideal heterodyne detection given by twice the CRLB, has yet to be experimentally demonstrated. To this end, we propose and implement a single-shot measurement for phase estimation of coherent states based on coherent displacement operations, single photon counting, and fast feedback. Our demonstration surpasses the limit of an ideal heterodyne measurement without correcting for detection efficiency in our implementation. This superior performance is achieved by real-time optimization of the displacement operation conditioned on the detection history as the measurement progresses. For this optimization, we show that the use of different objective functions yields similar results, which outperform an ideal heterodyne measurement.

(Session 9b : Sunday from 4:15pm - 4:45pm)